Make a Real Projective Plane (Boy’s Surface) out of Paper

I am teaching an undergraduate course in topology. We are now looking at what we get if we take a square and glue the sides together. (These are called identification spaces.) We are assuming that our spaces are made out of very stretchy rubber. So, if the space begins as a square, we could, for instance,…

The Magnificent Möbius Band

As I write this blog post, we are all either struggling with the impact of the COVID-19 virus or waiting nervously as cases start to rise in our area. I am currently teaching remotely. My college students are scattered around the globe, and we are interacting through various online methods. This semester I am teaching…

How to Present a Mathematical Proof or Problem

There are many useful websites containing advice on how to give a good mathematics presentation (such as those listed here). But these are written for scholars who are giving lectures on their research. They focus on organizing the talk, putting the research in context, deciding what to include or not include, designing slides, pacing and…

Homemade Klein Bottle

One of my favorite items in my collection of mathematical objects is a glass Klein bottle made by Cliff Stoll. So I was excited when—a few years ago—I saw that it was possible to make a glass-looking Klein bottle out of a Method soap bottle. Eventually, we bought some of this soap and then used…

Tales of Impossibility: Now Published!

I’m very excited to announce that my new book, Tales of Impossibility: The 2000-Year Quest to Solve the Mathematical Problems of Antiquity (Princeton University Press, 2019), is now available! (OK. It was published about a month ago, but I am just now getting around to blogging about it.) Like my previous book, Euler’s Gem (Princeton University…

BraidTiles—A Mathematical Braid Puzzle

We can view braids mathematically as n strings hanging from a horizontal bar.  Each piece of string runs downward and can cross neighboring strings. In the 1920s Emil Artin observed that braids of n strings form an algebraic group. To “multiply” two braids, we append the bottom of one braid with the top of another braid. The identity element in this group…

A Numerical Crossword Puzzle

I recently made my first crossword puzzle. It was great fun. It had some mathematical clues, but it was not mathematical. So for my second crossword puzzle, I decided to make one that was 100% mathematical. Download my numerical crossword puzzle in which each cell contains a decimal point ” . ” or a digit 0…

The Most Imaginary Number… is Real!

On the eve of “π Day,” a hush has fallen on the mathematical internet. Everyone is gearing up, getting ready to celebrate the beauty of the transcendental number π. Indeed, π is an amazing number. I have a book coming out in October about the geometric problems of antiquity (Tales of Impossibility: The 2000-Year Quest…

My First Crossword Puzzle

I recently discovered Phil, an HTML5 crossword puzzle maker (here it is on GitHub). I’ve always wanted to make a crossword puzzle, but it seemed overwhelming. But with Phil, I found it fun and addicting! So, here is my first creation. It has a mathematical theme. I’ve enjoyed solving crossword puzzles off and on over…

Make Your Own Pythagorean Cup

My parents recently went to Greece. They brought me back a souvenir—a practical joke cup called a “Pythagorean cup.” The legend behind the cup is that Pythagoras or one of the Pythagoreans invented this cup to prevent gluttony. The vessel looks like a cup with an odd pillar in the center. When you fill it…